The Filesystem, Explained

A filesystem is the tree of files and folders the OS lays over raw numbered storage; a path is an address into that tree, permissions decide who may touch each file, and a few simple rules explain almost every 'file not found' or 'permission denied' you'll ever hit.

1. What a Filesystem Is A disk is just numbered storage; the OS imposes a tree of folders and files on top of it, and a path is the address that walks you down that tree from the root to one file.
2. Permissions & Ownership Every file has an owner and rules for who can read, write, or run it; 'permission denied' means you tried to do something the rules don't allow you to - and that's a protection, not a punishment.
3. Where Things Live & Finding Them How the OS turns a path into real bytes, why hidden dotfiles and file extensions are just naming conventions, where standard things live, and how to find any file - with a cheat for the three classic errors.